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first transmission of L brazi liensis to a human volunteer by P. 

 paraensis (=Lu. pessoana ) the infective bite was merely a 30-sec probe 

 resulting in no blood ingestion. 



Transmissions by bite of Lu_. diabol ica and Lu. shannoni occurred 

 after a critical period of multiplication and development in the sand 

 fly, during which time a massive infection was established in the 

 region of the cardia and the stomodeal valve. This period corresponds 

 to the logarithmic phase of growth described in cultures (Sacks and 

 Perkins, 1984). Once this point in the life cycle of the parasite is 

 reached, division ceases and reduction in size of many promastigotes 

 to short-slender, highly active forms begins. This period corresponds 

 to the stationary phase of growth in cultures (Sacks and Perkins, 

 1984). The short-slender, highly active forms were first apparent in 

 the region of the cardia and stomodeal valve, and spread forward to 

 the pharynx and mouthparts, as well as rearward to the midgut and 

 hindgut. It is tempting to suggest that they represent a 

 morphologically distinct, highly infective stage. 



Sacks and Perkins (1984) stated that although morphological 

 differences between dividing midgut forms and those found anteriorly 

 have been described, there is no evidence that these changes reflect 

 development of promastigotes to an infective stage. They found, 

 however, that the infectivity of L donovani promastigotes taken from 

 stationary cultures greatly exceeded that of promastigotes from 

 cultures in the logarithmic phase. Further, they found that identical 

 developmental changes occurred during growth of promastigotes in the 

 fly. Leishmania tropica promastigotes, taken from the gut of infect 

 Lu . anthophora three days after fly infection, were essentially 



